Nabilone is the generic name for 6a,10a-1-hydroxy-3-(1,1-dimethylheptyl)-6,6-dimethyl-6,6a,7,8,10,10a-hexahydro-9H-dibenzo[b,d]pyran-9-one. The pharmaceutically active and marketed form of nabilone (and what is typically understood by the term nabilone) is trans-nabilone, namely 6a,10a-trans1-hydroxy-3-(1,1-dimethylheptyl)-6,6-dimethyl-6,6a,7,8,10,10a-hexahydro-9H-dibenzo[b,d]pyran-9-one:

Trans-nabilone is typically a racemic mixture consisting of the (6aS,10aS) and the (6aR,10aR) isomers.
Nabilone is a synthetic cannabinoid which mimics the main ingredient of marijuana (THC), though it is not derived from the cannabis plant. It is typically used for the treatment of chemotherapy-induced nausea and vomiting for patients that do not respond to conventional anti-emetics (anti-nausea medications). It has also been used in the treatment of anorexia and weight loss in patients with AIDS, and as an adjunct therapy for chronic pain management. Case studies have also demonstrated various benefits for conditions such as fibromyalgia and multiple sclerosis.
Nabilone is one of a class of compounds known as hexahydrodibenzopyranones. In view of the clinical usefulness of nabilone and related dibenzopyranones, efforts have been made to find improved and alternative methods for the preparation of such compounds. The original synthesis of 6a,10a-trans-hexahydrodibenzopyranones suffered from being multistep and of low overall yields, in addition to providing substantial mixtures of 6a,10a-cis and 6a,10a-trans isomers, the separation of which is difficult; see U.S. Pat. No. 3,507,885.
A three-step synthesis of 6a,10a-cis-hexahydrodibenzopyranones was published by Archer, et al., J. Org. Chem., 42, 2277 (1977). Archer et al. also provided a method for converting the 6a,10a-cis isomers to the corresponding 6a,10a-trans isomers; see U.S. Pat. No. 4,054,582 and Archer et al., J. Org. Chem., 42, 2277 (1977). Archer's synthesis is outlined below:

Large scale commercial use of the above synthesis is problematic. Archer et al use a classic Birch reduction in the first step, wherein the compound is reacted in liquid ammonia at −73° C. On a large scale, the use of such low temperatures, and the requirement for large quantities of liquid ammonia are not desirable. The second step is a condensation/annulation reaction in which tin chloride (SnCl4) is used as a Lewis acid catalyst. Because tin is toxic, its use in the reaction so close to the end product is problematic; any trace amounts of tin which may remain in the final product are not desirable for the purpose of human consumption and regulatory approval.
It is, therefore, desirable to provide an improved synthesis of hexahydrodibenzo[b,d]pyran-9-ones that avoids these problems.